Deoxidizing a heat of steel



United States Patent DEOXIDIZING A HEAT OF STEEL James Fernando Jordan, Huntington Park, Calif.

No Drawing. Application June 2, 1954, Serial No. 434,091

8 Claims. (Cl. 75-12) My invention relates to metallurgy wherein a heat of steel is to be deoxidized preparatory to casting.

This is a continuation-in-part of my applications: Serial No. 299,223 of July 16, 1952, now abandoned; Serial No. 310,913 of September 22, 1952, now abandoned; Serial No. 361,823 of June 15, 1953, now abandoned; Serial No. 403,932 of January 13, 1954, now abandoned; and Serial No. 411,005 of February 17, 1954, now pending.

Metallurgical literature contains numerous references to peculiarities in the behavior of steel made by the different practices. Thus, the basic electric processes are known to yield a steel that exhibits poor fluidity in the molten state and excellent physical properties once it has been solidified, While the acid electric processes, on the other hand, yield steel that exhibits physical properties which vary all the way from poor to fair and a fluidity that varies from poor to excellent. Seldom, if ever, do the physical properties of acid steel compare with those regularly obtained with basic steelthis, even in those cases wherein both steel types are of a similar chemical composition. between heats in each practice and between practices, is very large.

Metallurgists have commonly attributed these differences to many things. Some have discussed these variations in terms of differences in the amount of phosphorus, sulphur, hydrogen, nitrogen, oxygen, etc. present in the different steels, while others have attributed the differences to the effect of variations in the deoxidizer combinations employed and to different deoxidizer-addition rotations.

I have found another factor. This new factor concerns the maintenance of what may be called the balanced condition between the oxidizing effect of the oxygen content of the molten metal, on one hand, and the net deoxidizing effect of the deoxidizers present in the molten metal, on the other hand. I have found that when said balanced condition is maintained between deoxidation and casting, uniform results will always be obtained no matter which steel-making practice, acid or basic, is being employed. I have found that the use of my preferred embodiment renders the resulting steel remarkably insensitive to variations in the phosphorus, sulphur, hydrogen and nitrogen content of the steel.

Briefly, my deoxidizing practice involves adjusting the temperature of the bath, adding enough oxygen to the bath to develop a G0 boil, shutting off the power, adding an excess of the deoxidizers, and tapping the heat.

The temperature of the bath must be adjusted to the desired level early in the deoxidizing practice. The method to be employed in adjusting the bath temperature will, in general, depend upon whether the oxygen lance or iron oxide additions are to be employed to develop the C-0 boil.

In making a, say, S. A. E. 1030 type steel according to my practice, I charge in enough carbon to cause the bath to contain from, say, 0.35 to 0.40% carbon upon meltdown. Then, if iron ore or mill scale is to be employed for the C-0 boil, I do not begin the oreing-down operation until the arcs have lifted the bath to a temperature.

lying over the desired tapping temperature, perhaps from 50 to 100 F. thereover, whereupon I begin the oreingdown operation, adding the iron oxide in such increments as will cause the carbon to drop at a rate of about one point (0.01%) per minute until from to points of carbon have been eliminated, keeping the arcs on a low tap during the oreing-down operation.

With the bath lowered to below 0.25% carbon, and

The magnitude of such variations, both ice boiling strongly, I proceed with the deoxidation by completely turning off the power to the electrodes and stopping the iron oxide additions to the bath. In my preferred embodiment, the next step involves permitting the C-0 boil to quiet down into a gentle boil or simmer, an operation that is accelerated by keeping the furnace door closed, however, extreme care must be exercised in avoiding allowing the bath boil to stop, for whatever reason. By the time that the boil has quieted down to a gentle simmer, the laboratory will have reported back on the composition of the bath at the time that the electrodes were disconnected and the ore additions were stopped, a sample of the bath having been taken for this purpose when the ore additions were stopped.

With the bath boiling gently, and with the laboratory report adjusted to the further carbon loss that occurs as the bath boil quiets down, the operator is in a position to add his furnace deoxidizer(s). This is done by throwing the required amount of ferro-alloy(js) into the gently boiling bath to achieve the desired degree of furnace deoxidation, calling for the ladle at the same time, it being assumed that the ferro-alloy(s) will be dissolved/ melted by the time that the ladle has been brought into pouring position. It is to be noted that the heat content of the bath is depended upon to provide the heat necessary to dissolve/melt the ferro-alloy deoxidizer(s), the disconnection of the power to the electrodes at the time that the ore additions were stopped being a permanent disconnection, insofar as this particular heat is concerned.

At least two temperature tests should be made during the foregoing procedure-with an immersion pyrometer, preferably, or with the fluidity spiral, if desired. The first temperature test should be made before the C-0 boil is started, so as to assure a temperature level high enough to yield the desired temperature at tap; the second temperature test should be made after the ore additions are stopped, so as to assure the correctness of the assumptions involved in the first test.

I have observed that some prefer to gain the required temperature build up between melt-down and the completion of the ore additions by maintaining the electrodes on a high tap during the boil. Such a practice, while yielding acceptable results, is not my preferred embodiment and does not yield the best results.

When employing the oxygen or air lance for the oreingdown operation, instead of direct iron oxide additions, the tapping temperature must be approached differently than it is in the foregoing case, for the lancing operation is exothermic. In employing the lance, the rate of carbon drop and the total carbon drop, in producing the same class of steel, should be the same as in the foregoing case, however, the temperature build up before the boil is begun need not be as large, due to the heat released during a lanced boil. Ordinarily, with a 1 /2 ton are furnace, a bath temperature of about F. below the desired tapping temperature is about the right point to start a lanced boil, however, it will be recognized by those skilled in the art, that this starting temperature will depend upon the size of the bath and upon the silicon, manganese, etc. content of the bath at the beginning of the boil. In case of doubt, the lanced boil should be started with the bath too high, not too low; for, if the bath turns out to be too hot after deoxidation, it will not harm it to allow it to cool within the furnace or in the: ladle. With respect to the former, I have never observed a detrimental effect on the quality of the metal arising from merely allowing a well-made heat of deoxidized steel to stand for some time in the furnace, however, the cooling bath should not be held too long in the furnace, else the power will have to be turned back on, and, as shall be discussed later, this will ruin the heat.

It is not necessary to maintain the furnace on low tap when the lance is being employed to develop and maintain the boil, however, if desired, this may be done. When the bath has been boiled down to the desired carbon level, the heat is finished off as in the manner described in connection with the oreing-down operation, the important thing being to add the deoxidizer(s) with the bath boiling gently and with the power disconnected. In my preferred embodiment with a lanced heat, the power is permanently disconnected at the time that the lancing is started. The temperature tests in the lancing practice may be carried out in the manners and at the times suggested in connection with the oreing-down operation.

In my preferred embodiment, I turn off the power permanently while the bath is still boiling strongly, preferably at the aforementioned rate of one point loss per minute. However, acceptable results can be obtained so long as the power is not kept on after the furnace deoxidizer(s) are melted/dissolved in the bath. The earlier that the power is turned oif, the better will be the results. Another way to say this is that, once the deoxidizing practice is started, the power can be kept on only if the bath is boiling as the result of the C- reaction, never when the bath is not boiling as the result of said reaction.

The foregoing deoxidation practices have the effect of maintaining the molten metal in the balanced condition previously described. Obviously, when, as the first step, a boiling bath is specified, this has the effect of stipulating that the bath be saturated with oxygen. This is the starting point. If, now, anything is done to unsaturate the bath with respect to its oxidizer/deoxidizer balance, even momentarily, the balanced condition will be.

immediately destroyed, and the only way that the balance can be restored is by adding oxygen thereto until it is oxygen saturated-balancedagain. And there exists the factor of the degree of unbalance, the diamage arising from oxygen unsaturation of a bath being directly proportional to the degree of unbalance.

It is quite surprising how easy it is to unsaturate a heat. Take the matter of the low tap. All electric furnace operators employ the low tap to maintain a temperature status quo in the bath; that is, with a bath adjusted to some desired level, it is the conventional practice to place the electrodes on a low tap, the idea being that the heat input via the low tap will just offset the heat losses from the furnace arising from radiation, etc. Holding a bath on a low tap immediately ruins the metal lying under the arcs, for heating the deoxidized metal over the temperature at deoxidation unbalances the metal by unsaturating it with respect to oxygen.

I have found that heating a deoxidized bath to a temperature above the bath temperature at deoxidation results in a degree of unbalance proportional to the degree of superheat, and I have found that this unbalanced condition is permanent in the absence of a reoxidizing step. Thus, I have found that when a deoxidized bath is substantially lifted over the temperature at deoxidation and is then cooled back to said temperature at deoxidation, something has changed, for the heat no longer exhibits the qualities that it possessed before being raised to the higher temperature. It is hard to say what has caused this change, however, it is highly probable that the higher temperature caused some change in the reaction product species, resulting in the development of an oxygen deficiency in the bath, resulting in unbalancing the bath. It may be shown that the difference in the actual oxygen content of a balanced bath as compared to the actual oxygen content of an unbalanced bath is very small indeed; accordingly, one is forced to assume that the very large differences in the behavior of the two metals is not caused by the difference in the oxygen levels of the two metals, per se, but, rather, by the oxygen balance, for it may be shown that the balanced condition and the unbalanced condition may be obtained at different oxygen levels, depending upon the amount of deoxidizers present. Thus, a heat may be caused to be balanced or unbalanced whether the actual oxygen content of the heat is high or low.

Whatever the overall tempertature effect of the low tap may be, it heats the metal immediately under the arcs to very high temperature levels, and this highly-heated metal, in circulating back into the bath as a whole, ruins the bath as a whole. In the face of this, it will be realized that the high tap will quickly ruin the properties of the bath; for, as mentioned previously, the higher the temperature is raised, the greater the degree of unbalance. The reason why bench heats are frequently the poorest heats around a steel foundry is not due to the higher temperature of such heats, per se, but, rather, it is due to the conventional practice of holding such heats on a high tap until the ladle is brought up.

Heating a balanced, deoxidized heat with the arcs is only one of the ways that the balanced tiOndilion can be destroyed. Take the matter of adding a deficiency of a deoxidizer to a bath. saturated, a deoxidizer is added in such amounts that the percentage level of said deoxidizer is not raised as the result of the addition, then the oxygen content of the bath has been lowered without a compensating increase in the net deoxidizing effect of the deoxidizers present in the bath. This results in the unbalanced condition. If the electrodes contact the bath for a short period, or if finely-divided ferro-manganese is scattered on the surface of the slag lying on the metal bath until the manganese has lowered the iron oxide content of the slag until the slag begins to extract FeO from the metal lying therebeneath, the metal bath will be thrown off balance with respect to its oxygen content.

When the furnace deoxidizer(s) are added, they must be added in excess directly into the metal bath, which means that the deoxidizers(s) must be added in the form of lumps large enough to sink thin the slag layer and into direct ocntact with the metal. The deoxidizer addition should never be wetted in order to blast its way thru the slag the proper approach being to thin out the slag in the addition area by means of small lime additions. Insofar as slag deoxidization is concerned, it should be achieved thru the instrumentality of deoxidizing elements present in the metal bath, not as the result of direct deoxidizer additions to the slag. When the slag is deoxidized thru the instrumentality of elements dissolved in the bath, the balanced condition, if present originally, is maintained; for, as the net deoxidizing effect of the deoxidizers in the metal bath goes down, the oxygen level of the metal bath goes up, however, it should be pointed out that even this procedure can quickly unbalance a heat if two deoxidizers of widely different oxygen affinity are present in the bath as it lies in contact with a slag containing a large amount of iron oxide or manganese oxide.

Due to the large spread in the relative affinities of the various deoxidizers employed conventionally to kill a wild steel, and in view of the commonly-employed concentrations usedthat is, for example, a high percentage of manganese, a moderate percentage of silicon and a low percentage of aluminum. it is vital that there be a net gain in the percentage level of each deoxidizer employed, and it is vital that enough be added of each deoxidizer so that the oxidizing conditions surrounding the molten metal after deoxidization do not strip the metal of one of the added deoxidizers. If this happens, the resulting metal may be badly unbalanced. Many like to make their steel by adding the manganese, silicon and a portion of the aluminum in the furnace, the balance of the aluminumand sometimes more manganese and/or silicon, being added to the metal as it flows into the ladle. In view of the fact that the aluminum is far and away the most active deoxidizer present, and in view of the very low concentration of aluminum employed in steel-making practices, it does not take a black slag long to completely strip the metal of its aluminum content. Even if some small amount of aluminum remains in the metal as it flows into the ladle, the mixing action of the tapping operation, together with the exposure of the metal to air incidental to the tapping operation, are sure to strip the metal of its aluminum content-it being remembered that there is an appreciable delay before the ladle additions melt to enter the metal. During the interval between the tapping operation and the melting of the ladle addition of aluminum, the molten steel is, therefore, likely to conform to the situation wherein the aluminum is gone and the resulting metal must depend upon its silicon and manganese content for its balance against the oxygen content of the metal. The net deoxidizing effect of the usual concentrations of silicon and manganese is far below the effect of a mere trace of aluminum alone. When, then, enough oxygen is added to the metal to just strip it of its aluminum content, there is not enough oxygen present in the bath of metal to balance the metal with respect to the net deoxidizing effect of the manganese and silicon present. This defines the unbalanced condition. Thus, we have the paradoxical situation wherein an oxygen deficiency can be created by adding oxygen to a balanced metal. If the manganese and/or silicon content of the metal is high enough so that their net deoxidizing elfect equals or is greater than the effect of the prior aluminum level, then the heat may remain balanced as the aluminum is If, to a heat that is oxygen stripped therefrom, however, this would involve very high percentages of these less active deoxidizing elements, and is further complicated by variables introduced into the process by the various deoxidizer combinations.

The balanced condition, once destroyed, can only be restored by the addition of oxygen to the metal, never by the addition of further amounts of deoxidizers thereto. In this connection, it is interesting to point out that the upper portion of the metal in a ladle lies in contact with an oxidizing slag, and that such a slag will restore the balance in a metal otherwise unbalanced, however, such restoration will occur only in the upper portion of the ladle metal.

The foregoing species of metal unbalancing is in common evidence around the steel foundry employing green-sand practices. If conditions surrounding the metal are oxidizing enough to strip the molten steel of its aluminum content, the resulting steel castings will exhibit poor physical properties; but, if, on the other hand, the

oxidizing action is so strong that a portion of the silicon content of the metal is removed also, then the resulting castings will exhibit good physical properties. This is an example of unbalancing caused by the addition of oxygen to the metal, and of rebalancing caused by furlieved, by variations in the aluminum content of the steel. These changes in the habit of the precipitated sulphides are caused by changes in the oxygen balance, not by mere changes in the aluminum level, per se. Thus, as is well known, an aluminum level of about 0.02% can cause Type II sulphide inclusions or not, depending upon the method employed in making the steel, and 1t 1s the method of manufacture that controls the oxygen balance.

As mentioned previously, the actual dlfference in the oxygen content of a balanced steel and the oxygen content of an unbalance steel, assuming both are deoxidized with the usual amounts of manganese, silicon and aluminum, is so small that it defies analytical determination. In the face of this, the great differences between the two steels are hard to explain easy enough to explain the improved physical properties of the balanced steel by saying that an oxygen-saturated steel resists the absorption of hydrogen, I do not believe that this wholly explains the improvement, and I am sure that it does not explain the vastly improved fluidity of the molten metal, for how could such a minor amount of dissolved gas have such a marked effect? As the result of a detailed study of the habits of the precipitated sulphides in balanced vs. unbalanced heats, I have concluded that hydrogen has only a minor role in the behavior of these two metals, at least insofar as lowhumidity areas are concerned.

It has been observed by many that the addition of iron oxide to a molten steel of poor fluidity greatly improves the fiuidity of the steel. As a result of my study, I do not believe that oxygen ever directly improves the fluidity of molten steel, and I am convinced that the most fluid steel is always that metal which is essentially free from dissolved oxygen. a temperature just over the solidifying point, an oxygen-saturated metal contains less dissolved oxygen than an unsaturated metal, and I am convinced that the precipitating sulphides are responsible for this apparent paradox.

When the molten metal is unsaturated, the sulphides remain in solution until the final stages of the solidification process. When, however, the metal is saturated with oxygen, the sulphides precipitate just before the solidification process begins, with the result that a heterogeneous system consisting of two immiscible solvents is formed; that is, molten steel, on one hand, and molten sulphide particles, on the other hand. In such a system, the solute, FeO, distributes itself between the solvents in accordance with the relative solubility of FeO therein, and the efficiency of the extraction process While it is El It is my opinion that, at,

will depend upon the amount and the type of sulphides precipitated. Even tho the amount of sulphides precipitated may be quite low in such a system, the extraction efliciency can be quite high, due to the low solubility of FeO in the molten steel and the high solubility of FeO in the precipitated sulphides. This distribution ratio is under the control of those factors which control the solubility of FeO in the metal solvent, such as the type and quantity of deoxidizers present in the metal solvent, and those factors which control the species of the precipitated sulphides, such as the quantity of sulphur present and the presence of sulphide formers in the molten metal. Thus, an early sulphide shower will act to lower the FeO content of the metal below that value which might otherwise be assigned to the metal as the result of the presence in the bath of a given quantity of deoxidizeres. The difference in the oxygen content of a killed, balanced heat and the oxygen content of a killed, unbalanced heat is very small, so that this extraction process is brought into operation with a very small amount of additional oxygen, and this additional oxygen results in a metal with a lower oxygen content, due to the fact that it activates the extraction process.

As the molten steel cools to temperatures below the first appearance of the sulphide shower, the solubility of FeO and the sulphides is lowered, with the result that a further concentration of the metals FeO content into the separated sulphides occurs until, finally, at a temperature just over or at the solidifying point, the FeO content of the metal solvent is reduced to not quite zero.

Two factors seem to be necessary in order to gain an early sulphide shower: 1) the bath must be adjusted so that some sulphide is insoluble therein at some temperature during the cooling from the furnace temperature to the solidifying temperature, and (2) the bath must be seeded or inoculated with some compound that is capable of preventing super-saturation from holding up the sulphide precipitation. The former condition is set up by balancing the bath with respect to oxygen, and, in a bath containing silicon, as is the usual case, the latter is supplied by the silicon content of the bath as a falling temperature causes a never-ending shower of silicon dioxide particles to form in the bath, the reaction between the silicon and oxygen contents of the bath being favored by a falling temperature. It is believed that the adverse effect of the unbalanced condition arises from the effect of the silicon content of the bath on the precipitated SiOz particles; for, in heating a balanced heat by means of the arcs, the protection aiforded the precipitated SiOz particles by the oxygen saturated condition is removed, with the result that the silicon content of the bath reduces the SiOz content of the bath, at least in part, to SiO. Whatever the form of such SiO may be in the bath, it seems incapable of seeding the sulphide shower, indeed it seems to poison the precipitation. Once formed, SiOif this, indeed, be the compound involved, seems to resist the sort of oxidizing influence occasioned by a falling temperature, such as that obtained as a falling bath temperature oxidizes the silicon content of the bath to SiOz, the only Way to oxidize the SiO being by the addition of oxygen thereto.

Employing the foregoing reasoning in a series of tests, in conjunction with the known facts that a sulphide shower consisting of (Fe, Mn)S precipitates earlier than an aluminum sulphide shower and that such a (Fe, Mn)S shower proceeds best in a bath free from aluminum, I obtained my best results. Making a steel of the S. A. E. 4130 type, I deoxidized the balanced bath within the furnace at a temperature of about 3lO0 F. with the addition of 0.95% manganese and 0.50% silicon, and I tapped the metal into a ladle without the addition thereto of any aluminum. Positioning the ladle of metal near the mold, I held up the aluminum addition as long as possible, so as to permit the cooling process to precipitate a sulphide shower of (Fe, Mn)S, and then, just before pouring the metal into the mold, I added 0.10% aluminum, the pouring temperature being 2850 F. The castings produced by this procedure exhibited Type I inclusions and the highest ductility values that I obtained during my tests. Microscopic examination of the tests made in this way revealed little attack on the (Fe, Mn)S by the aluminum, as was expected, it being the thought that such a late addition of aluminum would cause an immediate increase in the FeO distribution ratio of the metal/ sulphide system by greatly lowering the solubility of FeO in the metal phase, and that the reaction between the precipitated sulphides and the aluminum would be slowed down by the heterogeneous nature of the system. As would be expected from such a late aluminum addition, aluminum oxide clusters were in plentiful evidence throughout the microstructure, however, the clusters were not associated with the critical grain boundary areas.

While most furnace deoxidizing procedures employ only manganese, or only manganese and silicon, or only manganese, silicon and aluminum, other deoxidizers and other deoxidizer combinations may be employed. Thus, zirconium may be substituted for manganese, all or in part, or titanium or zirconium may be substituted for aluminum, or calcium may be substituted for part of the aluminum. My deoxidizing procedure will prove eflective no matter which deoxidizers are employed.

In this specification, and in my claims, I always employ the term oxygen in the sense that it is the active reagent of the process, whether said oxygen is present in the molten steel as such or, as some believe, as FeO.

The following results were obtained in a 1 /2 ton electric arc furnace, acid lined:

(1) With the oxidizer/deoxidizers in balance (average of heats):

The practice followed in these 10 heats was uniformly in conformance with the following: employing a charge calculated to yield a bath of about 5000 lbs. upon melt down, the melting operation was carried out so that the bath contained about 0.25% carbon, 0.45% manganese and 0.20% silicon by the time that it had been raised to about 3000 F., there being no ore additions made during this preliminary heating operation. With the bath at temperature, the oxidizing procedure was started by charging in enough ore (mill scale) to develop a vigorous C-O boil, the electrodes being shifted to a low tap when the boil started. The boil was maintained by further ore additions until the carbon level fell to within the range between 0.10 and 0.15%, as determined by the fracture test, whereupon the power was turned off, the ore additions stopped, the ladle called for, and the furnace door closed. When the boil slowed down to a gentle simmer, about 200 lbs. of pig iron, 50 lbs. of ferro-silicon and 50 lbs. of ferro-manganese were thrown into the bath. When the ladle arrived, the bath was tapped into it, about 0.20% manganesein the form of ferro-manganese-and 0.10% aluminum being introduced into the ladle as the metal bath was tapped thereinto. It is to be noted that the bath was never heated after the boil was allowed to slow down, the heat content of the bath being sufiicient to accomplish the melting of the additions by the time that the ladle was brought up, nor was any particular attempt made to obtain a uniform mixture within the furnace. These heats were made during a period when the fluidity spiral was being experimented with as a means for determining the fluidity/temperature of the bath, and, as a consequence, some of the heats were checked with the spiral. some with the spoon test. In the latter cases, some effort towards mixing the bath was made during the sampling procedure. The fluidity/temperature checks were always made as the ladle was being swung into position.

As evidence of the effect of heating the bath after deoxidation, the following results are given:

(2) With the oxidizer/deoxidizers out of balance (average of heats):

Carbon 0.27%. Manganese 0.70%. Silicon a. 0.40%. Phosphorus 0.033%. Sulphur 0.035%.

Chromium 0.18%. Nickel 0.22%. Molybdenum 0.02%. Yield 52,400 p. s. i. Tensile 79,100 p. s. i. Elongation in 2" 19.8%. Reduction in area 22.5%.

The test bars of (l) and (2) were all heat treated together in the same furnace at the same time.

The heats of (2) were not deliberately made, being, rather, the result of various of the types of delay which occur occasionally around a steel plant-in these part1cular cases, the delay being so serious that the furnace had to be placed back on the high tap for about 10 minutes.

The heats of (1) and (2) were selected from much larger groups, the selection being made on the basis of similar chemical analyses, so as to exclude chemical analysis as an important variable-4n other words, all 25 heats were of a similar analysis. Nor were the results shown in (l) the best results obtained, if not being unusual for the elongation to run well over 30% and the reduction in area to run well over 65%. Nor were any of the bars of (l) or (2) aged at 400 F., as is the conventional practice in the industry.

When, in the basic-electric practices, the high-lime slag containing carbide has accomplished the desired degree of desulphurization, the pool of molten steel is out of balance with respect to the oxidizer/deoxidizers, for the carbide content of the slag has lowered the FeO content of the bath far below the level required to balance the usually low deoxidizer level therein, with the result that the metal exhibits poor fluidity. The balance may be restored, and a highly-fluid metal obtained, by introducing into the desulphurized metal bath sufficient oxygen to develop a G0 boil, and, once the boil is obtained, discontinuing heating the metal with the arcs and deoxidizing the bath as in the case of the acid practice. If, at the end of the desulphurizing period, the carbon level in the metal bath is so low that difiiculties are encountered in developing the C-0 boil, the situation may be cured by adding carbon to the bath before the oxygen-saturating operation is begun, and then continuing the boil until the carbon level has been restored to the desired level. While the oxygen-saturating operation may be carried out after the sulphur-containing slag has been flushed off, it will be found that flushing oil the slag gains little, for sulphur reversion from the slag to the metal bath during the oxygen-saturating operation will not be sufficient to seriously affect the quality of the metal.

My work with the oxidizer/deoxidizers balance has been restricted to the carbon and low-alloy steels. By low-alloy steels, I means steels containing no more than 3.50% of any one alloying element. I have tested my deoxidizing procedure with steels containing up to about 3.50% of chromium, manganese, nickel, silicon, etc., with uniformly successful results. For example, I have used the procedure to produce various of the steels of the S. A. E. Series: lxxx, Tl3xx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx and 9xxx, see page 612 of the Metals Handbook, 1939 edition, published by the American Society for Metals. My deoxidizing procedure may be employed advantageously to produce any of the aforementioned S. A. E. Series, or any similar carbon and low-alloy compositions, the latter being defined as a steel containing no more than about 3.50% of any one alloying element.

I claim as my invention:

1. In the process wherein carbon and low-alloy steels are produced on the hearth of a refractory-lined furnace from a pool of carbon-bearing molten steel that is heated thereon by means of electric arcs, the method of preparing said pool of molten steel for casting, which comprises: voluntarily introducing oxygen into reacting contact with said pool by charging iron oxide into said furnace until a boil breaks out within said pool as the result of the C-0 reaction; continuing said voluntary introduction of oxygen into said pool to lower the carbon content of said pool; stopping said voluntary introduction of oxygen into said pool; and adding an excess of at least one deoxidizing element to the boiling pool within said furnace so that the percentage of said element in said pool is higher after said addition than it was before said addition, said heating of said pool by means of said arcs being discontinued before said added element has completely dissolved in said pool so that the temperature of all of said pool falls continually from the time that said added element has dissolved in said pool until the time when said molten steel has been cast.

2. The method according to claim lin which said boil is a strong boil and in which said strong boil is allowed to quiet down into a gentle boil before said deoxidizing element is added to said pool.

3. The method according to claim 2 in which said arcs are disconnected at the height of said strong boil.

4. The method according to claim 2 in which said arcs are disconnected when said pool is boiling gently.

5. The method according to claim 1 in which said oxygen is introduced into said pool with a lance and in which said arcs are disconnected before said oxygen introduction is begun.

6. The method according to claim 1 in which said hearth is basic and in which said oxygen introduction into said pool is begun after said pool has been desulphurized by means of a high-lime slag containing carbide.

'10 7. The method according to claim 6 in which said ogrygen is introduced into said pool after a substantial portion of said carbide-containing slag has been removed from References Cited in the file of this patent Electric Furnace Steel Proceedings, vol. 7, pages 223, 246land 247. Published in 1948 by the A. I. M. E., New Yor Electric Furnace Steel Proceedings, vol. 8, page 108. Published in 1950 by the A. I. M. E., New York. 

1. IN THE PROCESS WHEREIN CARBON AND LOW-ALLOY STEELS ARE PRODUCED ON THE HEART OF A REFRACTORY-LINED FURNACE FROM A POOL OF CARBON-BEARING MOLTEN STEEL TAHT IS HEATED THEREON BY MEANS OF ELECTRIC ARCS, THE METHOD OF PREPARING SAID POOL OF MOLTEN STEEL FOR CASTING, WHICH COMPRISES: VOLUNTARILY INTRODUCING OXYGEN INTO REACTING CONTACT WITH SAID POOL BY CHARGING IRON OXIDE INTO SAID FURNACE UNTIL A BOIL BREAKS OUT WITHIN SAID POOL AS THE RESULT OF THE C-O REACTION; CONTINUING SAID VOLUNTARY INTRODUCTION OF OXYGEN INTO SAID POOL TO LOWER THE CARBON CONTENT OF SAID POOL; STOPPING SAID VOLUNTARY INTRODUCTION OF OXYGEN INTO SAID POOL; AND ADDING AN EXCESS OF AT LEAST ONE DEOXIDIZING ELEMENT TO THE BOILING POOL WITHIN SAID FURNACE SO THAT THE PERCENTAGE OF SAID ELEMENT IN SAID POOL IS HIGHER AFTER SAID ADDITION THAN IT WAS BEFORE SAID ADDITION, SAID HEATING OF SAID POOL BY MEANS OF SAID ARCS BEING DISCONTINUED BEFORE SAID POOL SO THAT THE TEMPERATURE OF PLETELY DISSOLVED IN SAID POOL SO THAT THE TEMPERATURE OF ALL OF SAID POOL FALLS CONTINUALLY FROM THE TIME THAT SAID ADDED ELEMENT HAS DISSOLVED IN SAID POOL UNTIL THE TIME WHEN SAID MOLTEN STEEL HAS BEEN CAST. 